Field
The present disclosure relates to a room pressure control system that keeps the pressure of a room constant through control of a supply air volume into the room and an exhaust air volume from the room.
Description of the Related Art
For example, in clean rooms in factories and laboratories, control is performed in which a room pressure (a differential pressure between rooms) is set for a room and the room pressure is kept constant to generate the air flow in an arbitrary direction for prevention of cross-contamination between rooms and assurance of safety by containment of hazardous substances.
Since it is necessary to frequently operate a room pressure control valve in order to keep the room pressure constant, there are problems in that the number of operations of the room pressure control valve is increased and the lifetime of the room pressure control valve is reduced.
Accordingly, in related art, provision of a control hold function while the room pressure is stable, in addition to a room pressure control function, to the room pressure control valve reduces the number of operations of the room pressure control valve and increases the lifetime of the room pressure control valve while the room pressure is kept constant (refer to Japanese Unexamined Patent Application Publication No. 2006-153325 and Japanese Unexamined Patent Application Publication No. 2012-237527). In the technologies disclosed in Japanese Unexamined Patent Application Publication No. 2006-153325 and Japanese Unexamined Patent Application Publication No. 2012-237527, dead zones are set around a set room pressure value and the operation of the room pressure control valve is stopped if a measured room pressure value is within the dead zones.
The steady short-period variation in the room pressure is naturally led to the original room pressure and the width of the variation is within a certain range in most cases. Accordingly, a dead zone width around the set room pressure value and a deviation time are set as dead zone parameters. If the measured room pressure value is within the range of the dead zone width or if the measured room pressure value has returned into the range of the dead zone width before the deviation time elapses even when the measured room pressure value has been out of the range of the dead zone width, the operation of the room pressure control valve is put on hold to increase the lifetime of the room pressure control valve.
Although the number of operations of the room pressure control valve is reduced and the lifetime of the room pressure control valve is increased with the technologies disclosed in Japanese Unexamined Patent Application Publication No. 2006-153325 and Japanese Unexamined Patent Application Publication No. 2012-237527, there are problems in that responsiveness of the control to fluctuation in the room pressure is reduced and the controllability of the room pressure is degraded.